1. Field of the Invention
The present invention relates to test device and more particularly, to a probing device for testing IC wafers.
2. Description of the Related Art
When testing an IC wafer, a probe card is used for transmitting test signals from a tester to the IC wafer. A typical conventional probe card comprises a circuit board for touchdown by the test head of a tester and receiving test signals from the tester, and a plurality of probes arranged in a high density manner at the center area of the bottom side of the circuit board for transmitting test signals from the circuit board to the IC wafer under test. After the probes touched down the electronic components of the IC wafer under test, test signals are transmitted from the tester to the electronic components of the IC wafer through the probe card, and measured signals are transmitted backwards from the electronic components of the IC wafer through the probe card to the tester for analysis. During the whole wafer level testing process, the circuit transmission design of the circuit board of the probe card greatly affects the test result. Following the development of electronic technology for high speed operation, the testing process must be run under a high speed environment. Therefore, the transmission circuit design must fit the requirements for high speed operation.
FIG. 1 illustrates a probe card design according to U.S. Pat. No. 5,808,475, entitled “Semiconductor probe card for low current measurements”. According to this design, the probe card 1 is formed from a contact board 10 disposed at the top side, a probe board 12 disposed at the bottom side, and spacers 14 set between the contact board 10 and the probe board 12. The contact board 10 is provided with coaxial cable-like test contacts 11 to avoid leakage current problem due to formation of parasitic resistance in the dielectric structure. However, because the contact board 10 is touched down by the test head of the tester 1′ directly and the probe board 12 is for the mounting of probes 13, the stress produced at the probe card 1 when the test head of the tester 1′ touching down the contact board 10 and the probes 13 touching down the IC wafer under test may cause the contact board 10 or the probe board 12 to deform due to uneven distribution of pressure if the contact board 10 or the probe board 12 itself isn't provided with an sufficient structural strength and/or an certain thickness. Further, when the probes 13 touching down the IC wafer, the front side of the probe board 12 keeps bearing the reaction force from the IC wafer. Under the effect of this reaction force, the structure of the front plane of the probe board 12 that holds the probes 13 may deform easily.
FIG. 2 illustrates another prior art design of probe card 2. According to this design, the probe card 2 comprises a multi-layer printed circuit board 20 and a plurality of probes 22. The multi-layer printed circuit board 20 has multiple circuit lines 21 extending from the outer side toward the inner side and from the top toward the bottom and then respectively electrically connected to the probes 22 that suspending below the multi-layer printed circuit board 20. The structural strength and single thrust surface design of the multi-layer printed circuit board 20 can averagely disperse the force received from the test sample when bearing the stress from the test head of the tester, preventing deformation. However, because the multi-layer printed circuit board 20 is a lamination of multiple layers of glass fiber or ceramic material and because each layer has metal wires arranged thereon to form the circuit lines 21, the fabrication of this design of probe card is complicated, requiring much cost and labor time. Further, when arranging the circuit lines 21 in the multi-layer printed circuit board 20, the material of the multi-layer printed circuit board 20 in between each two adjacent circuit lines 21 may cause a leakage current. Further, the via holes 210 of the multi-layer printed circuit board 20 through which the circuit lines 21 extend tend to cause interface reflection during transmission of test signals, resulting in energy loss. These drawbacks greatly affect high frequency transmission characteristics. Therefore, this design of probe card does not meet the requirements for high speed test of integrated electronic components.